Dr. Mabrouk is preparing polyethylene glycol (PEG) modified cytochrome c, microperoxidase-11 and horseradish peroxidase in efforts which are hoped to ultimately facilitate enzyme drug therapy. In the course of these studies, Dr. Mabrouk has "pioneered" the use of non-aqueous media for characterization of the modified enzymes. Analyses initiated at MIT and subsequently conducted at BUSM have demonstrated that MALDI-TOF MS is capable of providing molecular weight information of the starting proteins, polymer and adducts. The improved mass resolution and accuracy afforded by the Finnigan MAT Vision 2000 have been important for these measurements because the mass difference between PEG variants is 5000 Da and the peak width is broad due to the polymer distribution of the PEG.